LTC4056-4.2_15 Datasheet, PDF (13/16 Pages) Linear Technology – Linear Li-Ion Charger with Termination in ThinSOT

LTC4056-4.2
TYPICAL APPLICATIO S
USB Charging
The applications shown in Figures 5 and 6 are USB Li-Ion
chargers with automatic PowerPath^TM control. In order to
comply with USB power specifications a Li-Ion battery
charger must be able to limit the current draw from the
USB power port to 500mA, operate at input voltages as low
as 4.75V (ignoring resistive drops in the cable and connec-
tors which further reduce this value to 4.4V), and have a
low current standby mode.
As described in Undervoltage Charge Current Limiting, the
LTC4056 will automatically reduce charge current if the
input supply voltage reaches V_UVCL (typically 4.575V).
This feature ideally solves the additional 350mV of resis-
tive drop that the USB power specification requires. If an
LTC4056 is connected to a particularly resistive USB
cable, then charge current will be reduced to ensure that
the input voltage does not drop below the undervoltage
lockout threshold.
The TIMER/SHDN pin can be used to put the LTC4056 into
a low current standby mode. By pulling TIMER/SHDN to
GND, the LTC4056 and LTC4412 will draw about 50µA to
60µA combined from the USB power port.
The LTC4056 actually regulates the current delivered to
the I_SENSE pin (rather than the BAT pin current). This fact
allows the 500mA maximum USB power port consump-
tion to be easily enforced by tying all system loads to the
I_SENSE pin and programming the charger to supply just
under 500mA (Figures 5 and 6 are programmed for
490mA). The total impedance between the V_CC pin and
I_SENSE pin is typically 0.2Ω, so the maximum drop is just
100mV (at 500mA).
PowerPath is a trademark of Linear Technology Corporation.
USB
POWER
ON 0FF
R1
750Ω
M1
2N7002
RED
8
LTC4056
1
CHRG
V_CC
7
2
TIMER/SHDN I_SENSE
6
3
BAT
DRIVE
5
PROG
R2
4
GND
1.87k
C1
C4
1µF
4.7µF
R5
0.5Ω
M2B
1/2 IRF7329
Q1
ZXT1M322
BAT
M2A
1/2 IRF7329
C3
1µF
C2
+ ^0.1µF
Li-Ion
V_IN SENSE
LTC4412
GND GATE
CTL STAT
R3
470k
4056-4.2 F05
SYSTEM
LOAD
Figure 5. USB Charging and Automatic PowerPath Control with Auxiliary P-Channel MOSFET for Lowest Loss
USB
POWER
ON 0FF
R1
750Ω
M1
2N7002
RED
8
LTC4056
1
CHRG
V_CC
7
2
TIMER/SHDN I_SENSE
6
3
BAT
DRIVE
5
PROG
R2
4
GND
1.87k
C1
C4
1µF
4.7µF
R5
0.5Ω
MBRS130LT3
Q1
ZXT1M322
BAT
C3
1µF
C2
+ ^0.1µF
Li-Ion
V_IN SENSE
LTC4412
GND GATE
CTL STAT
M2
Si2315BDS
R4
750Ω
SYSTEM
LOAD
GREEN
R3
470k
M3
Si1301DL
4056-4.2 F06
Figure 6. USB Charging and Automatic PowerPath Control with LTC4412 in Comparator Mode
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